Dedicated outdoor air system with pre-heating and method for same

ABSTRACT

An energy exchange system is provided that may include a heater configured to be disposed within a supply air flow path. A first pre-heater is configured to be upstream from the heater within the supply air flow path and configured to pre-heat the supply air with a first liquid that circulates through the first pre-heater. A boiler may be operatively connected to the first pre-heater and configured to heat the first liquid. The system may also include a second pre-heater configured to be upstream from the heater within the supply air flow path. A heat transfer device may be operatively connected to the heater and the second pre-heater. The heat transfer device is configured to receive flue gas from the heater and transfer heat from the flue gas to a second liquid within the heat transfer device.

BACKGROUND OF THE DISCLOSURE

Embodiments of the present disclosure generally relate to a dedicatedoutdoor air system (DOAS) having one or more pre-heaters.

Enclosed structures, such as occupied buildings, factories and animalbarns, and the like generally include an HVAC system for conditioningventilated and/or recirculated air in the structure. The HVAC systemincludes a supply air flow path and a return and/or exhaust air flowpath. The supply air flow path receives air, for example outside orambient air, re-circulated air, or outside or ambient air mixed withre-circulated air, and channels and distributes the air into theenclosed structure. The air is conditioned by the HVAC system to providea desired temperature and humidity of supply air discharged into theenclosed structure. The exhaust air flow path discharges air back to theenvironment outside the structure, or ambient air conditions outside thestructure. Without energy recovery, conditioning the supply airtypically requires a significant amount of auxiliary energy. This isespecially true in environments having extreme outside air conditionsthat are much different than the required supply air temperature andhumidity. Accordingly, energy exchange or recovery systems are typicallyused to recover energy from the exhaust air flow path. Energy recoveredfrom air in the exhaust flow path is utilized to reduce the energyrequired to condition the supply air.

Conventional energy exchange systems may utilize energy recovery devices(for example, energy wheels and permeable plate exchangers) or heatexchange devices (for example, heat wheels, plate exchangers, heat-pipeexchangers and run-around heat exchangers) positioned in both the supplyair flow path and the exhaust air flow path. A Dedicated Outdoor AirSystem (DOAS) is an energy exchange system that conditionsambient/outside air to desired supply air conditions through acombination of heating, cooling, dehumidification, and/orhumidification.

In extremely cold conditions, however, frost may form on one or moreenergy recovery devices within a DOAS. For example, in extremely coldconditions, frost may form on an enthalpy wheel that first encountersoutside air within the DOAS. Frost on the enthalpy wheel typicallyreduces the efficiency and effectiveness of the enthalpy wheel.

Additionally, in extremely cold conditions, a heater of a DOAS may drawincreased power over a relatively long period of time in order toadequately heat air that is ultimately supplied to an enclosedstructure. As such, the energy requirements and costs of operation ofthe heater may increase.

SUMMARY OF THE DISCLOSURE

Certain embodiments of the present disclosure provide an energy exchangesystem that may include an energy recovery device, at least one firstpre-heater, and at least one boiler. The energy recovery device isconfigured to be disposed within supply and exhaust air flow paths. Thefirst pre-heater(s) is configured to be positioned within one or both ofthe supply and exhaust air flow paths, and may include one or more coilsconfigured to circulate a first liquid, such as water, that isconfigured to transfer heat to air within the supply and/or exhaust airflow paths. The boiler(s) is operatively connected to the firstpre-heater(s) and is configured to heat the first liquid.

The first pre-heater(s) may be configured to be upstream of the energyrecovery device within the supply air flow path.

The system may also include a heater or heat exchanger configured to bedownstream of the energy recovery device within the supply air flowpath. The first pre-heater(s) may be configured to be positioned withinthe supply air flow path between the energy recovery device and theheater.

The boiler(s) may include a main tank configured to retain the firstliquid. The boiler(s) may also include a heating element configured toheat the first liquid.

The first pre-heaters may include multiple first pre-heaters configuredto be positioned within the supply air flow path. The multiple firstpre-heaters may be operatively connected to a single boiler.Alternatively, each of the first pre-heaters may be connected toseparate and distinct boilers.

The energy exchange system may also include at least one secondpre-heater configured to pre-heat air within one or both of the supplyand exhaust air flow paths, a heater configured to be disposed withinthe supply air flow path, wherein the heater is configured to generateflue gas, and a heat transfer device operatively connected to the heaterand the at least one second pre-heater. The heat transfer device isconfigured to receive energy from the flue gas from the heater andtransfer heat from the flue gas to a second liquid, such as water,within the heat transfer device. The second liquid is configured to bechanneled to the second pre-heater(s) so that heat is transferred fromthe second liquid to supply air within the supply air flow path beforethe supply air encounters the energy recovery device.

The heater may be downstream from the energy recovery device within thesupply air flow path. Alternatively, the heater may be upstream from theenergy recovery device within the supply air flow path. The firstpre-heater(s) may be positioned with the supply air flow path betweenthe energy recovery device and the heater.

The energy exchange system may also include at least one bypass ductconfigured to be disposed within the supply air flow path. The bypassduct(s) is configured to bypass at least a portion of the supply airaround one or both of the at least one first pre-heater or the energyrecovery device.

Certain embodiments of the present disclosure provide a method ofoperating an energy exchange system having a supply air flow path thatallows supply air to be supplied to an enclosed structure and an exhaustair flow path that allows exhaust air from the enclosed structure to beexhausted to the atmosphere. The method may include heating a firstliquid within an internal chamber of a boiler, pumping the first liquidfrom the boiler to at least one first pre-heater disposed within one orboth of the supply air flow path and the exhaust air flow path,pre-heating air within the one or both of the supply air flow path andthe exhaust air flow path with the first liquid within the at least onefirst pre-heater, and pumping the first liquid from the at least onefirst pre-heater back to the boiler.

The method may also include capturing flue gas generated by a heater,channeling the flue gas to a heat transfer device, transferring heatfrom the flue gas to a second liquid within the heat transfer device,circulating the second liquid to at least one second pre-heater disposedwithin one or both of the supply air flow path and the exhaust air flowpath, and transferring heat within the second liquid to the air withinone or both the supply air flow path and the exhaust air flow path.

Certain embodiments of the present disclosure provide a DOAS that mayinclude a heater configured to be disposed within a supply air flowpath, a first pre-heater configured to be upstream from the heaterwithin the supply air flow path, wherein the first pre-heater isconfigured to pre-heat the supply air through heat transfer with a firstliquid that circulates through the first pre-heater, and a boileroperatively connected to the first pre-heater, wherein the boiler isconfigured to heat the first liquid. The DOAS may also include a secondpre-heater configured to be upstream from the heater within the supplyair flow path, and a heat transfer device operatively connected to theheater and the second pre-heater. The heat transfer device is configuredto receive flue gas from the heater and transfer heat from the flue gasto a second liquid within the heat transfer device. The second liquid isconfigured to be channeled to the second pre-heater so that heat istransferred from the second liquid to supply air within the supply airflow path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of an energy exchange system,according to an embodiment of the present disclosure.

FIG. 2 illustrates a simplified internal view of a boiler, according toan embodiment of the present disclosure.

FIG. 3 illustrates an isometric view of a coil of a pre-heater,according to an embodiment of the present disclosure.

FIG. 4 illustrates an isometric view of a coil of a pre-heater,according to an embodiment of the present disclosure.

FIG. 5 illustrates an isometric view of a coil of a pre-heater,according to an embodiment of the present disclosure.

FIG. 6 illustrates an isometric view of a coil of a pre-heater,according to an embodiment of the present disclosure.

FIG. 7 illustrates a schematic view of the energy recovery device,according to an embodiment of the present disclosure.

FIG. 8 illustrates a schematic view of an energy exchange system,according to an embodiment of the present disclosure.

FIG. 9 illustrates a schematic view of an energy exchange system,according to an embodiment of the present disclosure.

FIG. 10 illustrates a schematic view of an energy exchange system,according to an embodiment of the present disclosure.

FIG. 11 a illustrates a schematic view of a heat exchanger, according toan embodiment of the present disclosure.

FIG. 11 b illustrates a schematic view of a heat exchanger, according toan embodiment of the present disclosure.

FIG. 12 illustrates an isometric top view of an exemplary furnace,according to an embodiment of the present disclosure.

FIG. 13 illustrates a schematic view of an energy recovery system,according to an embodiment of the present disclosure.

FIG. 14 illustrates a schematic view of an energy recovery system,according to an embodiment of the present disclosure.

FIG. 15 illustrates a schematic view of an energy recovery system,according to an embodiment of the present disclosure.

FIG. 16 illustrates a process of operating a direct outdoor air system,according to an embodiment of the present disclosure.

FIG. 17 illustrates a process of operating a direct outdoor air system,according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofcertain embodiments will be better understood when read in conjunctionwith the appended drawings. As used herein, an element or step recitedin the singular and proceeded with the word “a” or “an” should beunderstood as not excluding plural of said elements or steps, unlesssuch exclusion is explicitly stated. Furthermore, references to “oneembodiment” are not intended to be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Moreover, unless explicitly stated to the contrary,embodiments “comprising” or “having” an element or a plurality ofelements having a particular property may include additional suchelements not having that property.

As explained below, embodiments of the present disclosure provide anenergy exchange system that may include one or more pre-heatersconfigured to pre-heat supply air before an energy recovery deviceand/or a heat exchanger, such as a heater. Accordingly, embodiments ofthe present disclosure provide an energy exchange system that operatesmore efficiently than known systems.

FIG. 1 illustrates a schematic view of an energy exchange system 10,according to an embodiment of the present disclosure. The system 10 isshown as a Dedicated Outdoor Air System (DOAS). The system 10 isconfigured to partly or fully condition air supplied to an enclosedstructure 12, such as a building or an enclosed room. The system 10includes an air inlet 14 fluidly connected to a supply air flow path 16.The supply air flow path 16 may channel supply air 18 (such as outsideair, air from a building adjacent to the enclosed structure 12, orreturn air from a room within the enclosed structure 12) to the enclosedstructure 12. Supply air 18 in the supply air flow path 16 may be movedthrough the supply air flow path 16 by a fan or fan array 20. The fan 20may be located downstream of an energy recovery device 22 and apre-heater 24. Optionally, the fan 20 may be positioned upstream of theenergy recovery device 22 and/or the pre-heater 24. Also, alternatively,supply air 18 within the supply air flow path 16 may be moved bymultiple fans or a fan array or before and/or after the pre-heater 24.

Airflow passes from the inlet 14 through the supply air flow path 16where the supply air 18 first encounters the pre-heater 24. A bypassduct 26 may be disposed in the supply air flow path 16. The bypass duct26 may be connected to the supply air flow path 16 through an inletdamper 28 upstream from the pre-heater 24, and an outlet damper 30downstream from the pre-heater 24. When the dampers 28 and 30 are fullyopened, supply air 18 may be diverted or bypassed around the pre-heater26. The dampers 28 and 30 may be modulated to allow a portion of thesupply air 18 to bypass around the pre-heater 26. Alternatively, thesystem 10 may not include the bypass duct 26.

Additionally, a damper 32 may be disposed in the supply air flow path 16upstream from the pre-heater 24. When fully closed, the damper 32prevents supply air 18 from passing into the pre-heater 24. The damper32 may be modulated in order to allow a portion of the supply air 18 topass through the pre-heater 24, while a remaining portion of the supplyair 18 is bypassed through the bypass duct 26. Alternatively, the system10 may not include the damper 32

The pre-heater 24 heats the supply air 18 is it passes therethrough. Thepre-heater 24 heats the incoming supply air 18 before it encounters theenergy recovery device 22. An additional pre-heater may be disposedwithin the supply air flow path 16 downstream from the pre-heater 24 andupstream or downstream from the energy recovery device 22. Theadditional pre-heater is configured to add more heat to the supply air18 during extremely cold conditions. The pre-heater 24 may,alternatively, be disposed within an exhaust air flow path 40 upstreamfrom the energy recovery device 22. Additionally, alternatively, apre-heater may also be disposed within the exhaust air flow path 40upstream from the energy recovery device 22. As explained in more detailbelow with respect to FIG. 7, the energy recovery device 22 uses exhaustair 42 from the exhaust flow path 40 to condition the supply air 18within the supply air flow path 16. For example, during a winter modeoperation, the energy recovery device 22 may condition the supply air 18within the supply air flow path 16 by adding heat and/or moisture. In asummer mode operation, the energy recovery device 22 may pre-conditionthe supply air 18 by removing heat and moisture from the air. While theenergy recovery device 22 is shown downstream from the pre-heater 24within the supply air flow path 16, the energy recovery device 22 may,alternatively, be positioned upstream of the pre-heater 24 within thesupply air flow path 16.

After the supply air 18 passes through the energy recovery device 22 inthe supply air flow path 16, the supply air 18, which at this point hasbeen conditioned, may encounter a heat exchanger 44, such as a heater.The heat exchanger 44 then further heats the supply air 18 in the supplyair flow path 16 to generate a change in air temperature toward adesired supply state that is desired for supply air discharged into theenclosed structure 12. For example, during a winter mode operation, theheat exchanger 44 may further condition the pre-conditioned air byadding heat to the supply air 18 in the supply air flow path 16.

The exhaust or return air 42 from the enclosed structure 12 is channeledout of the enclosed structure 12, such as by way of exhaust fan 46 orfan array within the exhaust flow path 40. As shown, the exhaust fan 46is located upstream of the energy recovery device 22 within the exhaustair flow path 40. However, the exhaust fan 46 may be downstream of theenergy recovery device 22 within the exhaust air flow path 40. Theexhaust air 42 passes through a regeneration side or portion of theenergy recovery device 22. The energy recovery device 22 is regeneratedby the exhaust air 42 before conditioning the supply air 18 within thesupply air flow path 16. After passing through the energy recoverydevice 22, the exhaust air 42 is vented to atmosphere through an airoutlet 48.

In an alternative embodiment, additional bypass ducts and dampers may bedisposed within the supply air flow path 16 and/or the exhaust air flowpath 40 in order to bypass airflow around the energy recovery device 22.

The pre-heater 24 is operatively connected to a boiler 50. The boiler 50provides heated liquid, such as water, to the pre-heater 24 in order topre-heat the supply air 18 within the supply air flow path 16. Thepre-heater 24 may include one or more coils 51 that surround a portionof the supply air flow path 16. The coils 51 are configured to channelheated liquid, such as water, from an inlet 52 to an outlet 54. Theinlet 52 connects to a liquid outlet 56 of the boiler 50 through aliquid delivery line 57, such as a conduit, tube, duct, or the like.Similarly, the outlet 54 connects to a liquid inlet 58 of the boiler 50through a liquid reception line 59, such as a conduit, tube, duct, orthe like. One or more pumps 60 may be disposed within the liquiddelivery and/or reception lines 57, 59 in order to move the liquidbetween the boiler 50 and the coils 51 of the pre-heater 24.

In operation, the boiler 50 heats liquid within a tank of the boiler 50.The heated liquid is then delivered to the coils 51 of the pre-heater 24by way of the liquid delivery line 57. The boiler may heat the liquid,such as water, to a temperature of approximately 180° F. As such, theheated liquid may not boil, but instead remain in a liquid state as itis pumped into the coils 51. The heated liquid within the coils 51exchanges energy with the supply air 18 as the supply air passes throughthe pre-heater 24. The heat from the liquid is transferred to the supplyair 18, thereby increasing the temperature of the supply air 18, butreducing the temperature of the liquid within the coils 51. Thereduced-temperature liquid passes out of the outlet 54 into the liquidreception line 59, which, in turn, channels the reduced-temperatureliquid back to the boiler 50. The boiler 50 then re-heats thereduced-temperature liquid, and the process repeats. Accordingly, thepre-heater 24 heats the supply air 18 before the supply air 18encounters the energy recovery device 22. The boiler 50 provides heatedliquid, such as heated water, to the coils 51 of the pre-heater 24 sothat the pre-heater 24 can pre-heat the supply air 18 before itencounters the energy recovery device 22 and the heat exchanger 44.

As shown, the pre-heater 24 is positioned upstream from the energyrecovery device 22 within the supply air flow path 16. Alternatively,the pre-heater 24 may be downstream from the energy recovery device 22within the supply air flow path 16. Additionally, the pre-heater 24 maybe downstream from the heat exchanger 44 within the supply air flow path16. As such, the pre-heater 24 may be a heating device that is apost-heater. Also, alternatively, additional pre-heaters may be disposedwithin the supply air flow path 16. For example, an additionalpre-heater may be disposed between the pre-heater 24 and the energyrecovery device 22 within the supply air flow path 16. Also, additionalpre-heaters may be disposed with the supply air flow path 16 between theenergy recovery device 22 and the heat exchanger 44, and/or downstreamfrom the heat exchanger 44. Each of the pre-heaters within the system 10may be operatively connected to respective boilers. Alternatively,multiple pre-heaters may be operatively connected to a single boiler.

Additionally, alternatively, the boiler 50 may be operatively connectedto the heat exchanger 44, such as through conduits, pipes, or the like,so that flue gas from the boiler 50 is provided to the heat exchanger44. The higher temperature flue gas from the boiler 50 may be used toheat fluid, whether air or water, within the heat exchanger 44. Thus,the boiler 50 may directly heat air within the supply air flow path 16,as well as provide heated flue gas to the heat exchanger 44, which alsoheats air within the supply air flow path. Moreover, the heat exchanger44 and/or the boiler 50 may also be operatively connected to apre-heater disposed within the exhaust air flow path 40 upstream fromthe energy recovery device 22. Accordingly, the heat exchanger 44 andvented flue gas from the boiler 50 may also be used to condition airwithin the exhaust air flow path 40.

FIG. 2 illustrates a simplified internal view of the boiler 50,according to an embodiment of the present disclosure. The boiler 50includes a main tank 70 defining an internal chamber 72 that retains aliquid 73, such as water. A heating element 74 may be positionedproximate the base of the main tank 70 and is configured to heat theliquid 73 within the internal chamber 72. The heating element 74 may bean electric or gas heater, for example. While shown proximate the baseof the main tank 74, the heating element 74 may be positioned at orwithin any portion of the main tank 70. For example, the heating element74 may include electric heating coils positioned within walls thatdefine the main tank 70.

The internal chamber 72 is in fluid communication with the liquid outlet56 and the liquid inlet 58. Accordingly, heated liquid may be pumpedthrough the liquid outlet 56, into the liquid delivery line 57, and intothe pre-heater 24 (shown in FIG. 1). Similarly, reduced-temperatureliquid may be pumped through the liquid reception line 59, into theliquid inlet 58, and into the internal chamber 72.

An exhaust port 76 may be formed through a portion of the main tank 70.The exhaust port 76 is configured to allow steam within the internalchamber 72 to pass out of the internal chamber 72. Alternatively, themain tank 70 may not include the exhaust port 76. Additionally, theboiler 50 may also include a chimney 78 configured to exhaust anycombustion gases, such as flue gases, generated by the heating element74. Alternatively, the chimney 78 may be connected to a flue gasdelivery line, which may be used to increase the temperature of thesupply air, such as through an additional pre-heater, for example, asexplained below.

The boiler 50 may be one or more of various types of boilers. Forexample, the boiler 50 may be a fire tube boiler, water tube boiler,packaged boiler, fluidized bed combustion boiler, atmospheric fluidizedbed combustion boiler, pressurized fluidized bed combustion boiler,atmospheric circulating fluidized bed combustion boiler, stoker firedboiler, pulverized fuel boiler, waste heat boiler, thermic fluid heater,hydronic boiler, and/or the like. As noted, FIG. 2 merely illustrates asimplified configuration for a boiler. Any type of boiler that isconfigured to heat liquid may be used. As noted, the boiler 50 may beoperated to heat the liquid below a boiling point in order to provideheated liquid to the coils 51 (shown in FIG. 1) of the pre-heater 24.

FIG. 3 illustrates an isometric view of a coil 51 a of the pre-heater24, according to an embodiment of the present disclosure. As shown inFIG. 3, the coil 51 a may be a tubular member 80 having acircumferential channel 82 surrounding an air passage 84, which may be aportion of the supply air flow path 16 (shown in FIG. 1). Liquid, suchas water or glycol, is circulated through the circumferential channel82. In this manner, liquid L may flow parallel to the supply air 18 asit passes through the air passage 84. Optionally, the liquid may flow ina direction counter to the direction of the air flow (in this example,the lines L would flow in the opposite direction than shown in FIG. 3).

FIG. 4 illustrates an isometric view of a coil 51 b of the pre-heater24, according to an embodiment of the present disclosure. In thisembodiment, a plurality of tubes 86 having fluid channels 88 surround anair passage 90, which may be a portion of the supply air flow path 16(shown in FIG. 1). Liquid L, such as water or glycol, is circulatedthrough the fluid channels 88. In this manner, liquid may flow parallelto the supply air 18 as it passes through the air passage 90.Optionally, the liquid may flow in a direction counter to the directionof the air flow.

FIG. 5 illustrates an isometric view of a coil 51 c of the pre-heater24, according to an embodiment of the present disclosure. In thisembodiment, the coil 51 c may include a series of fluid-filled plates 92disposed within an air passage 94 that forms part of the supply air flowpath 16 (shown in FIG. 1). In this manner, the supply air 18 may flowacross and parallel or counter to the liquid within the plates 92.

FIG. 6 illustrates an isometric view of a coil 51 d of the pre-heater24, according to an embodiment of the present disclosure. In thisembodiment, the coil 51 d includes a plurality of liquid-carrying tubes96 that cross one another. The tubes 96 are disposed within an airpassage 98 that forms part of the supply air flow path 16 (shown in FIG.1). In this manner, the supply air 18 may flow across and parallel orcounter to the liquid L within the tubes 96.

Any of the coils shown and described with respect to FIGS. 3-6 may beused with respect to the pre-heater 24, heat exchanger, heater, or othersuch heat transfer device.

Referring to FIGS. 1-6, the pre-heater 24 may be configured forparallel-flow, counter-flow, cross-flow, or a combination thereof. Thecoils 51 shown in FIG. 1 may include any of the coils 51 a, 51 b, 51 c,and/or 51 d. In parallel flow, the supply air 18 and the liquid withinthe coils 51 enter the pre-heater 24 at the same end, and travelparallel to one another to the other side. In counter-flow, the supplyair 18 enters at a front end of the pre-heater 24, while the liquidenters the coils 51 at the back end. In cross-flow, the supply air 18and the liquid within the coil are generally perpendicular to oneanother within the pre-heater 24. Therefore, while FIG. 1 shows theliquid delivery line 57 at a downstream end of the pre-heater 24, andthe liquid reception line 59 at an upstream end of the pre-heater 24, itis understood that these positions may be reversed.

The pre-heater 24 and the boiler 50 may be retrofit to any DOAS, therebyimproving the efficiency of the DOAS.

FIG. 7 illustrates a schematic view of the energy recovery device 22,according to an embodiment of the present disclosure. A portion of theenergy recovery device 22 is disposed within the supply air flow path16, while another portion of the energy recovery device 22 is disposedwithin the exhaust air flow path 40. The energy recovery device 22 isconfigured to transfer heat and/or moisture between the supply air flowpath 16 and the exhaust air flow path 40. The energy recovery device 22may be one or more of various types of energy recovery devices, such as,for example, an enthalpy wheel, a sensible wheel, a desiccant wheel, aplate heat exchanger, a plate energy (heat and moisture) exchanger, aheat pipe, a run-around loop, or the like. As shown in FIG. 7, theenergy device 22 may be an enthalpy wheel.

An enthalpy wheel is a rotary air-to-air heat exchanger. As shown,supply air within the supply air flow path 16 passes in a directioncounter to the exhaust air within exhaust air flow path 40. For example,the supply air may flow through a lower portion, such as the lower half,of the wheel, while the exhaust air flows through an upper portion, suchas the upper half, of the wheel. Alternatively, supply air may flowthrough a different portion of the wheel, such as a lower ⅓, ¼, ⅕, orthe like, of the wheel, while exhaust air flows through the remainingportion of the wheel. The wheel may be formed of a heat-conductingmaterial with an optional desiccant coating.

In general, the wheel may be filled with an air permeable materialresulting in a large surface area. The surface area may be the mediumfor sensible energy transfer. As the wheel rotates between the supplyand exhaust air flow paths 16 and 40, respectively, the wheel picks upheat energy and releases it into the colder air stream. Enthalpyexchange may be accomplished through the use of desiccants on an outersurface of the wheel. Desiccants transfer moisture through the processof adsorption, which is driven by the difference in the partial pressureof vapor within the opposing air streams.

Additionally, the rotational speed of the wheel also changes the amountof heat and moisture transferred. For example, an enthalpy wheeltransfers both sensible and latent energy. The slower the rate ofrotation, the less moisture is transferred.

The enthalpy wheel may include a circular honeycomb matrix ofheat-absorbing material that is rotated within the supply and exhaustair flow paths 16 and 40, respectively. As the enthalpy wheel rotates,heat is picked up from the air within the exhaust air flow path 40 andtransferred to the supply air within the supply air flow path 16. Assuch, waste heat energy from the air within the exhaust air flow path 40is transferred to the matrix material and then from the matrix materialto the supply air 18 within the supply air flow path 16, thereby raisingthe temperature of the supply air 18 by an amount proportional to thetemperature differential between the air streams.

Optionally, the energy recovery device 22 may be a sensible wheel, aplate exchanger, a heat pipe, a run-around apparatus, a refrigerationloop having a condenser and evaporator, a chilled water coil, or thelike.

Alternatively, the energy recovery device 22 may be a flat plateexchanger. A flat plate exchanger is generally a fixed plate that has nomoving parts. The exchanger may include alternating layers of platesthat are separated and sealed. Because the plates are generally solidand non-permeable, only sensible energy may be transferred. Optionally,the plates may be made from a selectively permeable material that allowsfor both sensible and latent energy transfer.

Alternatively, the energy recovery device 22 may be a run-around loop orcoil. A run-around loop or coil includes two or more multi-row finnedtube coils connected to each other by a pumped pipework circuit. Thepipework is charged with a heat exchange fluid, typically water orglycol, which picks up heat from the exhaust air coil and transfers theheat to the supply air coil before returning again. Thus, heat from anexhaust air stream is transferred through the pipework coil to thecirculating fluid, and then from the fluid through the pipework coil tothe supply air stream.

Also, alternatively, the energy recovery device 22 may be a heat pipe. Aheat pipe includes a sealed pipe or tube made of a material with a highthermal conductivity such as copper or aluminum at both hot and coldends. A vacuum pump is used to remove all air from the empty heat pipe,and then the pipe is filled with a fraction of a percent by volume ofcoolant or refrigerant, such as water, ethanol, glycol etc. Heat pipescontain no mechanical moving parts. Heat pipes employ evaporativecooling to transfer thermal energy from one point to another by theevaporation and condensation of a working fluid or coolant.

Referring again, to FIG. 1, as supply air 18 enters the supply air flowpath 16 through the inlet 14, the unconditioned supply air 18 encountersthe pre-heater 24 before the energy recovery device 22, which may be anenthalpy wheel, flat plate exchanger, heat pipe, run-around, or thelike, as discussed above. During winter months, when the air is cold anddry, the temperature and/or humidity of the supply air 18 will be raisedas it moves through the pre-heater 24 and encounters the energy recoverydevice 22. As such, in winter conditions, the energy recovery device 22warms and/or humidifies the supply air.

A similar process occurs as the exhaust air 42 encounters the energyrecovery device 22 in the exhaust air flow path 40. The sensible and/orlatent energy transferred to the energy recovery device 22 in theexhaust air flow path 40 is then used to pre-condition the air withinthe supply air flow path 16. Overall, the energy recovery device 22pre-conditions the supply air 18 in the supply air flow path 16 beforeit encounters the heat exchanger 44, and alters the exhaust air 42 inthe exhaust air flow path 40. In this manner, the heat exchanger 44 doesnot use as much energy as it normally would if the energy recoverydevice 112 (and/or the pre-heater 24) was not in place. Therefore, theheat exchanger 44 operates more efficiently.

The heat exchanger 44 may be or include a gas heater that coverts gas toheat, for example. Alternatively, the heater exchanger may be configuredto transfer heat from liquid to air, for example. That is, the heatexchanger 44 may be a liquid-to-air heat exchanger. In general, theliquid and air are separated so that they do not mix. The heat exchanger44 may include radiator coils that are positioned within or around thesupply air flow path 16. Liquid, such as water or glycol, may becirculated through the coils. As supply air 18 passes by the coils, heatfrom the liquid is transferred to the supply air 18, thereby furtherwarming the supply air 18 before it passes into the enclosed structure12. The radiator coils may be heated through combustion, for example,such as through a gas-fired heater. Heated gas from the heater is ventedas flue gas. As explained below, the vented flue gas may be channeled toa heating device, such as another pre-heater, in order to pre-conditionthe supply air 18 before it encounters the energy recovery device 22, asdescribed in U.S. patent application Ser. No. 13/625,912, entitled“Dedicated Outdoor Air System With Pre-Heating And Method For Same,”which was filed Sep. 25, 2012, and is hereby incorporated by referencein its entirety. Alternatively, the heat exchanger 44 may not includeradiator coils, but may simply be a gas heater disposed within thesupply air flow path 16, and configured to convert gas to heat and heatthe supply air 18.

FIG. 8 illustrates a schematic view of an energy exchange system 800,according to an embodiment of the present disclosure. The energyexchange system 800 is similar to the system 10, except that apre-heater 802, which is operatively connected to a boiler 804, isdownstream from an energy recovery device 806 and upstream from a heatexchanger 808 within a supply air flow path 810. The pre-heater 802 andthe boiler 804 may be configured to operate as described above.

Alternatively, the pre-heater 802 may be downstream from the heatexchanger 808 within the supply air flow path 810. Also, an additionalpre-heater may be positioned within the supply air flow path 810upstream from the energy recovery device 806. The additional pre-heater802 may be operatively connected to the boiler 804, or to a separate anddistinct boiler.

FIG. 9 illustrates a schematic view of an energy exchange system 900,according to an embodiment of the present disclosure. The energyexchange system 900 is similar to the system 10, except that the system900 includes a pre-heater 902 upstream from an energy recovery device904 within a supply air flow path 906, as well as a pre-heater 908downstream from the energy recovery device 904, but upstream from a heatexchanger 910, within the supply air flow path 906. The pre-heaters 902and 908 may both be operatively connected to a common boiler 912.Separate and distinct liquid delivery lines 914 and 916 connect theboiler 912 to each of the pre-heaters 910 and 902, respectively.Optionally, a single liquid delivery line may extend from the boiler 912and branch off to the separate and distinct pre-heaters 910 and 902.Similarly, liquid reception lines 918 and 920 may connect thepre-heaters 902 and the 908, respectively, to the boiler 912. The liquidreception lines 918 and 920 may merge together, as shown in FIG. 8, intoa single line 922 that channels reduced-temperature liquid from eachpre-heater 902 and 908 into the boiler 912. Alternatively, separate anddistinct liquid reception lines may connect directly to the boiler 912.

FIG. 10 illustrates a schematic view of an energy exchange system 1000according to an embodiment of the present disclosure. The system 1000 isconfigured to partly or fully condition air supplied to an enclosedstructure 1002, such as a building or an enclosed room. The system 1000includes an air inlet 1004 fluidly connected to a supply air flow path1006. The supply air flow path 1006 may channel supply air 1008 (such asoutside air, air from a building adjacent to the enclosed structure1002, or return air from a room within the enclosed structure 1002) tothe enclosed structure 1002. Supply air 1008 in the supply air flow path1006 may be moved through the supply air flow path 1006 by a fan or fanarray 1010. The illustrated embodiment shows the fan 1010 locateddownstream of an energy recovery device 1012 and a gas-fired heater orheat exchanger 1014. The heat exchanger 1014 may be or include thegas-fired heater. Optionally, the fan 1010 may be positioned upstream ofthe energy recovery device 1012 and/or the heat exchanger 1014. Also,alternatively, air 1008 within the supply air flow path 1006 may bemoved by multiple fans or a fan array or before and/or after the heatexchanger 1014.

Airflow passes from the inlet 1004 through the supply air flow path 1006where the supply air 1008 first encounters a pre-heater 1009 operativelyconnected to a boiler 1011, as described above. The pre-heater 1009 maybe upstream from a pre-heater 1016 with the supply air flow path 1006.Optionally, the pre-heater 1016 may be upstream from the pre-heater 1009within the supply air flow path 1006.

A bypass duct 1017 may be disposed in the supply air flow path 1006downstream or upstream from the pre-heater 1009. The bypass duct 1017may be positioned in the supply air flow path 1006 between thepre-heaters 1009 and 1016. The bypass duct 1017 may be connected to thesupply air flow path 1006 through an inlet damper 1019 upstream from thepre-heater 1016 (but downstream from the pre-heater 1009), and an outletdamper 1021 downstream from the pre-heater 1016. Alternatively, theinlet damper 1019 may be upstream from the pre-heater 1009 within thesupply air flow path 1006. When the dampers 1019 and 1021 are fullyopened, supply air 1008 may be diverted or bypassed around thepre-heater 1016 (and/or the pre-heater 1009). The dampers 1019 and 1021may be modulated to allow a portion of the supply air 1008 to bypassaround the pre-heater 1016 (and/or the pre-heater 1009).

Additionally, a damper 1023 may be disposed in the supply air flow path1006 upstream from the pre-heater 1016 and/or the pre-heater 1009. Whenfully closed, the damper 1023 prevents supply air 1008 from passing intothe pre-heater 1016 and/or the pre-heater 1009. The damper 1023 may bemodulated in order to allow a portion of the supply air 1008 to passthrough the pre-heater 1016 and/or the pre-heater 1009, while aremaining portion of the supply air 1008 is bypassed through the bypassduct 1017.

The pre-heater 1009 heats the air 1008 as it passes therethrough, asexplained above with respect to FIGS. 1 and 2, for example.Additionally, the pre-heater 1016 heats the air 1008 is it passestherethrough. The pre-heater 1016 heats the incoming supply air 1008before it encounters a process side or portion of the energy recoverydevice 1012. An additional pre-heater may be disposed within the supplyair flow path 1006 downstream from the pre-heater 1016 and upstream fromthe energy recovery device 1012. The additional pre-heater is configuredto add more heat to the supply air 1008 during extremely coldconditions. The pre-heater 1016 may, alternatively, be disposed withinan exhaust air flow path 1020 upstream from the energy recovery device1012. Additionally, alternatively, a pre-heater may be disposed withinthe exhaust air flow path 120 upstream from the energy recovery device1012 as well as the pre-heater 1016 within the supply air flow path1006. As explained above, the energy recovery device 1012 uses exhaustair 1018 from the exhaust flow path 1020 to condition the supply air1008 within the supply air flow path 1006. An additional energy recoverydevice (not shown) may be positioned within the supply air flow path1006 downstream from the heat exchanger 1014, and upstream from theenclosed structure 1002. Additionally, while the energy recovery device1012 is shown upstream from the heat exchanger 1014 within the supplyair flow path 1006, the energy recovery device 1012 may, alternatively,be positioned downstream of the heat exchanger 1014 and upstream of theenclosed structure 1002 within the supply air flow path 1006.Additionally, the positions of the pre-heaters 1009 and 1016 may bereversed, such that the pre-heater 1009 is downstream from thepre-heater 1016 within the supply air flow path 1006.

After the supply air 1008 passes through the energy recovery device 1012in the supply air flow path 1006, the supply air 1008, which at thispoint has been conditioned, encounters the heat exchanger 1014. The heatexchanger 1014 then further or fully heats the air 1008 in the supplyair flow path 1006 to generate a change in air temperature toward adesired supply state that is desired for supply air discharged into theenclosed structure 1002. For example, during a winter mode operation,the heat exchanger 1014 may further condition the pre-conditioned air byadding heat to the supply air 1008 in the supply air flow path 1006.

The exhaust or return air 1018 from the enclosed structure 1002 ischanneled out of the enclosed structure 1002, such as by way of exhaustfan 1022 or fan array within the exhaust flow path 1020. As shown, theexhaust fan 1022 is located upstream of the energy recovery device 1012within the exhaust air flow path 1020. However, the exhaust fan 1022 maybe downstream of the energy recovery device 1012 within the exhaust airflow path 1020.

The exhaust air 1018 passes through a regeneration side or portion ofthe energy recovery device 1012. The energy recovery device 1012 isregenerated by the exhaust air 1018 before conditioning the supply air1008 within the supply air flow path 1006. After passing through theenergy recovery device 1012, the exhaust air 1018 is vented toatmosphere through an air outlet 1024.

In an alternative embodiment, additional bypass ducts and dampers may bedisposed within the supply air flow path 1006 and/or the exhaust airflow path 1020 in order to bypass airflow around the energy recoverydevice 1012.

The supply air 1008 encounters the pre-heater 1016 before the energyrecovery device 1012, which may be an enthalpy wheel, flat plateexchanger, heat pipe, run-around, or the like, as discussed above. Thepre-heaters 1009 and 1016 pre-heat the supply air 1008, and the energyrecovery device 1012 pre-conditions the supply air 1008 in the supplyair flow path 1006 before the supply air 1008 encounters the heatexchanger 1014. In this manner, the heat exchanger 1014 does not use asmuch energy as it normally would if the pre-heaters 1009, 1016, and theenergy recovery device 1012 were not in place. Therefore, the heatexchanger 1014 operates more efficiently.

The heat exchanger 1014 may be or include a gas heater that coverts gasto heat, for example. Heated gas from the heater is vented as flue gas.As explained below, the vented flue gas is channeled to the pre-heater1016 in order to pre-condition the supply air 1008 before it encountersthe energy recovery device 1012.

In general, flue gas is a gaseous combustion product from a furnace orheating device. The flue gas may be formed primarily of nitrogen (forexample, more than ⅔) derived from the combustion of air, carbondioxide, and water vapor, as well as excess oxygen, which is alsoderived from the combustion of air.

FIG. 11 a illustrates a schematic view of the heat exchanger 1014,according to an embodiment. As noted above, the heat exchanger 1014 isdisposed within the supply air flow path 1006. The heat exchanger 1014may be a heater that includes a housing 1026 that contains a gas-firedheater 1028, such as a furnace. Optionally, a boiler as described abovemay be used in place of the gas-fired heater 1028. The heater 1028 maygenerate heat through combustion. The heater 1028 heats the supply air1008 as it passes through the heat exchanger 1014 within the supply airflow path 1006. As supply air 1008 passes through the heat exchanger1014, the temperature of the supply air 1008 increases as it is heatedby the heater 1028. Consequently, the temperature of the supply air 1008is increased as it passes out of the heat exchanger 1014.

The flue gas from the heater 1028 is vented through a vent 1032 on orwithin the housing 1026. The heat exchanger 1014 may include a fan (notshown) that channels the flue gas into the vent 1032. Optionally, thefan may be disposed downstream of the vent 1032 within a conduit 1034.The conduit 1034 may be one or more pipes, tubes, plenum, or the like.For example, the conduit 1034 may be a series of pipes that connect thevent 1032 to another heat transfer device. The flue gas from the vent1032 then passes into the conduit 1034 that sealingly engages the vent1032 so that the flue gas may be channeled to another heat transferdevice, as described below.

Alternatively, the heat exchanger 1014 may include radiator coils thatcontain circulating liquid, such as water, that is heated by the heater1028. The heated liquid exchanges heat energy with the supply air 1008as it passes through the radiator coils 1030. The radiator coil may beconfigured as shown and described in FIGS. 3-6.

FIG. 11 b illustrates a schematic view of a heat exchanger, according toan embodiment of the present disclosure. The heat exchanger 1114 may bedisposed within a supply air flow path 1106. The heat exchanger 1114includes a housing 1126 that contains a boiler 1128 and radiator coils1130 that contain a liquid, such as water, that is heated by the boiler1128. The boiler 1128 may generate heat through combustion. The boiler1128 heats liquid that circulates through the radiator coils 1130. Theradiator coils 1130 are positioned within and/or around the portion ofthe supply air flow path 1106 that passes through the heat exchanger1114. As supply air 1108 passes through the heat exchanger 1114, thetemperature of the supply air 1108 increases as it passes through theradiator coils 1130. That is, the heat of the liquid within the radiatorcoils 1130 is transferred to the supply air 1108. Consequently, thetemperature of the supply air 1108 is increased as it passes out of theheat exchanger 1114.

The flue gas from the boiler 1128 is vented through a vent 1132 on orwithin the housing 1126. The heat exchanger 1114 may include a fan (notshown) that channels the flue gas into the vent 1132. Optionally, thefan may be disposed downstream of the vent 1132 within a conduit 1134.The conduit 1134 may be one or more pipes, tubes, plenum, or the like.For example, the conduit 1134 may be a series of pipes that connect thevent 1132 to another heat transfer device. The flue gas from the vent1132 then passes into the conduit 1134 that sealingly engages the vent1132 so that the flue gas may be channeled to another heat transferdevice, as described below.

FIG. 12 illustrates an isometric top view of an exemplary furnace 1029,according to an embodiment of the present disclosure. The furnace 1029is one example of a heater 1028 (shown in FIG. 11). The furnace 1029includes a housing 1027 having a plurality of heating elements 1031 thatspan between lateral walls 1033 of the housing 1027. The heatingelements 1031 may include channeled rods having openings through whichflames pass, thereby generating heat. The furnace 1029 may be connectedto a source of gas (not shown) that fuels the furnace 1029. As gasenters the heating elements 1031 and is ignited through an ignitingelement or pilot light within a control section 1035, flames aregenerated. Additionally, flue gas is also generated from the heatingelements. The temperature of the flame generated by the heating elements1031 may be approximately 2700° F., which generates a flue gastemperature of approximately 400° F. Various other furnaces may be usedas the heater 1028. FIG. 12 merely shows one example of a furnace.

The heating elements 1031 may include tubes that contain gas that isignited to produce heat. The gas may make several passes through thetubes before passing to the vent 1032, shown in FIG. 11. As air withinthe supply air flow path 1006 passes over the tubes 1031, the air isheated.

Smaller tubes may be disposed within each of the tubes. For example, amain gas tube may surround a concentric liquid tube that contains heattransfer liquid. The liquid tube may be in fluid communication with thepre-heater 1016 and/or the pre-heater 1009, shown in FIG. 10. In thismanner, the heat transfer liquid may be directly heated within thefurnace and transferred to the pre-heater 1016 and/or the pre-heater1009 to heat the supply air 1006. As such, the temperature of the heattransfer liquid may be increased as it is directly heated within thefurnace 1029 and directly transferred to the pre-heater.

Referring to FIGS. 10 and 11, flue gas from the heat exchanger 1014 isvented to the conduit 1034. The conduit 1034 channels the flue gas to aheat transfer device 1060, such as a heating coil, that may include aninternal coil structure, similar to those described above.Alternatively, the flue gas may be transferred to a heating elementwithin the boiler 1011 instead of, or in addition to, the heat transferdevice 1060. The heated flue gas passes through an internal chamber (notshown) of the heat transfer device 1060 and/or the boiler 1011. As theflue gas passes through the heat transfer device 1060 and/or the boiler1011, the heat from the flue gas is transferred to the liquid within theradiator coils of the heat transfer device 1060 and/or the internalchamber of the boiler 1011. The decreased-temperature flue gas (as heatfrom the flue gas has been transferred to the liquid) is then vented tothe atmosphere through a vent 1062, for example (or through a chimney ofthe boiler 1011, as described with respect to FIG. 2). However, theliquid within the radiator coil of the heat transfer device 1060, havingan increased temperature through heat transfer with the flue gas, ischanneled to the pre-heater 1016 through a conduit 1064. The heatedliquid is then passed from the conduit 1064 into an inlet 1065 of a coil1066 of the pre-heater 1016. The pre-heater 1016 may also includeradiator coils similar to those described above with respect to FIGS.3-6. The liquid passed into the coil 1066, the temperature of which hasrisen due to the heat transfer with the flue gas, then transfers theincreased heat to supply air 1008 that passes through the pre-heater1016. Accordingly, the supply air 1008 is pre-heated (that is, thetemperature of the supply air 1008 is increased) before it encountersthe energy recovery device 1012.

As the liquid within the coil 1066 circulates therethrough, thetemperature of the liquid decreases, as its heat is transferred to thesupply air 1008. The cooled liquid within the radiator coil 1066 passesout of the radiator coil 1066 through an outlet 1067 and into a conduit1068 that connects back to the heat transfer device 1060. The liquid isthen heated again by heat transfer with the flue gas, and the processrepeats.

A pump 1070 may be disposed within either of the conduits 1064, 1068, orboth. The pump(s) 1070 aids in circulating the liquid between the heattransfer device 1060 to the pre-heater 1016. However, in at least oneembodiment, the system 1000 does not include the pump.

While the pre-heaters 1009, 1016, and the heat transfer device 1060 aredescribed as including liquid-conveying coils, the pre-heaters 1009,1016 and the heat transfer device 1060 may be, or include, various otherliquid-carrying and/or heating structures and components. For example,the pre-heater 1016 may include fluid-conveying plates. Similarly, theheat transfer device 1060 may be a heating plate(s). Additionally, eachof the pre-heaters 1009, 1016 and the heat transfer device 160 may alsoinclude separate and distinct heating devices, similar to the heater1028 shown in FIG. 11. However, the liquid that is circulated betweenthe heat transfer device 1060 and the pre-heater 1016 may be primarilyor solely heated by way of heat transfer with the flue gas. Optionally,the liquid that is circulated between the heat transfer device 1060 andthe pre-heater 1016 may be also heated through an electric heater.

Additionally, while the heat transfer device 1060 is shown as beingseparate, distinct, and remote from the heat exchanger 1014 and thepre-heater 1016, the heat transfer device 1060 may be contained within ahousing of the heat exchanger 1014 or the pre-heater 1016. For example,the heat transfer device 1060 may be mounted directly to the vent of theheat exchanger 1014 inside or outside of the housing of the heatexchanger 1014. As such, the heat exchanger 1014 and the heat transferdevice 1060 may be disposed within a common housing.

The supply air 1008 (for example, air supplied from outdoor and/orambient air) is pre-heated by the pre-heaters 1009 and 1016. Thepre-heaters 1009 and 1016 increase the temperature of the supply air1008 so that it will not form frost on the energy recovery device 1012.The pre-heater 1016 may increase the temperature of the supply air 1008through a circulating liquid that has been heated through a transfer ofheat from harvested flue gas, as described above. As such, theefficiency of the system 1000 is increased. Additionally, thepre-heaters 1009 and 1016 provide a more efficient system, in that theypre-heat the supply air 1008, thereby reducing the overall energyconsumption of the downstream heat exchanger 1014 to further heat thesupply air 1008.

Moreover, the pre-heaters 1009 and 1016 and the heat transfer device1060 may be retrofit to any DOAS, thereby improving the efficiency ofthe DOAS.

FIG. 13 illustrates a schematic view of an energy recovery system 1380,according to an embodiment of the present disclosure. The system 1380 issimilar to the system 1000, except that a heat exchanger 1314 isupstream from an energy recovery device 1312 within a supply air flowpath 1306. Additionally, a heating device 1301 operatively connected toa boiler 1303 may be downstream from the energy recovery device 1312within the supply air flow path 1306. Because the heating device 1301 isdownstream from the energy recovery device 1312 and the heat exchanger1314, the heating device 1301 may not be considered a pre-heater.However, the heating device 1301 may be configured to operate as thepre-heaters described above. Further, the heating device 1301 may bepositioned at various other portions of the supply air flow path 1036,such as between a pre-heater 1316 and the heat exchanger 1314, orbetween the heat exchanger 1314 and the energy recovery device 1312.

As shown in FIG. 13, the supply air 1308 is further heated after thepre-heater 1316 before the supply air 1308 encounters the energyrecovery device 1312. Thus, the possibility of frost forming on theenergy recovery device 1312 is further reduced. The system 1380 may alsoinclude an additional heat exchanger downstream from the energy recoverydevice 1312 within the supply air flow path 1306.

FIG. 14 illustrates a schematic view of an energy recovery system 1490,according to an embodiment. The energy recovery system 1490 is similarto the system 1000, except that an additional heat exchanger 1492 ispositioned upstream the energy recovery device 1412, and a pre-heater1401 operatively connected to a boiler 1403 is downstream from theenergy recovery device 1412 and upstream from a heat exchanger 1414within the supply air flow path 1406. The heat exchanger 1492 may be aliquid-to-gas heat exchanger. Flue gas from both the heat exchangers1414 and 1492 is vented into a shared conduit 1494 that channels thecombined flue gas into a coil heater 1460. The pre-heater 1401 and theboiler 1403 may be configured to operate as described above. The system1490 may include additional pre-heaters 1401 and boilers 1403.

Alternatively, the pre-heater 1401 may be positioned at various otherportions of the supply air flow path 1406. For example, the pre-heater1401 may be positioned between a pre-heater 1416 and the heat exchanger1492, or between the heat exchanger 1492 and the energy recovery device1412.

Additionally, in all of the embodiments of the present disclosure, anoptional return air duct may connect an exhaust air flow path 1420 withthe supply air flow path 1406. For example, an air duct may bedownstream of the energy recovery device 1412 in the supply air flowpath 1406, and upstream of the energy recovery device 1412 in theexhaust air flow path 1420. Alternatively, or additionally, anadditional return air duct may be upstream of the energy recovery device1412 in the supply air flow path 1406 and downstream of the energyrecovery device 1412 within the exhaust air flow path 1420. The returnair ducts may recycle a portion of the exhaust air 1418, which may be ata much higher temperature than outdoor air, into the supply air 1408,which further increases the temperature of the supply air 1408.

FIG. 15 illustrates a schematic view of an energy recovery system 1500,according to an embodiment of the present disclosure. The system 1500 issimilar to the system 1000, except that return air ducts 1502, 1504, and1506 connect an exhaust air flow path 1520 to a supply air flow path1506. More or less return air ducts than those shown may be used.Moreover, the return air ducts may be used with any of the systemsdescribed above.

Additionally, a pre-heater 1501 operatively connected to a boiler 1503may be disposed within the supply air flow path 1506 between an energyrecovery device 1512 and a heat exchanger 1514. The pre-heater 1501 andthe boiler 1503 are configured to operate as described above. Thepre-heater 1501 may be disposed at various other portions of the supplyair flow path 1506. For example, the pre-heater 1501 may be disposedbetween a pre-heater 1516 and the energy recovery device 1512.Additional pre-heaters 1501 and boilers 1503 may also be used.

The return air duct 1506 connects to the supply air flow path 1506upstream of the pre-heater 1516. Thus, the temperature of the supply air1508 may be increased even before it encounters the pre-heater 1516.

FIG. 16 illustrates a process of operating a direct outdoor air system,according to an embodiment. At 1620, flue gas from a heat exchanger orheater is vented and captured within a conduit. The flue gas may bemoved through the use of a fan, for example.

At 1622, the flue gas is channeled to a heating device, such as aheating coil, plate, another heat exchanger, furnace, or the like. Next,at 1624, the heat within the flue gas is transferred to liquid containedwithin the heating device. As the flue gas passes through the heatingdevice and decreases in temperature (as the heat from the flue gas istransferred to the liquid within the heating device), the flue gas isvented from the heating device at 1626. At the same time, at 1628, theliquid, having an increased temperature due to heat transfer with theflue gas, is circulated to a pre-heater, which may include aliquid-circulating coil. Then, at 1630, the heated liquid within thepre-heater is circulated around supply air flowing through a supply airflow path. Heat within the liquid is transferred to the supply air. Atthis time, the temperature of the liquid decreases, as a portion of itsheat is transferred to the supply air. The liquid fully circulatesthrough the pre-heater and is then recirculated back to the heatingdevice at 1632, and then the process returns to 1624.

Additionally, flue gas and/or liquid may be bypassed to control theamount of energy transfer. Moreover, the flow of liquid may be modulatedto control the amount of energy transfer.

FIG. 17 illustrates a process of operating a direct outdoor air system,according to an embodiment. At 1700, liquid within a boiler is heated.The liquid may be heated below a boiling point. Next, at 1702, theheated liquid is pumped from the boiler to one or more coils of apre-heater disposed within a supply air flow path. The pre-heater may bedisposed within any portion of the supply air flow path (and/or withinany portion of an exhaust air flow path). Further, the heated liquid maybe pumped to multiple pre-heaters.

At 1704, heat from the heated liquid is transferred to air within thesupply air flow path. As the heated liquid moves through the coil(s),the temperature of the liquid decreases, as the heat is transferred tothe air. As such, reduced-temperature liquid is pumped from the coil(s)of the pre-heater back to the boiler at 1706. The process then returnsto 1700.

The processes of FIGS. 16 and 17 may occur in conjunction with oneanother. Each process may be performed simultaneously, or one of theprocesses may occur before the other.

Thus, embodiments provide systems and methods of heating air within asupply air flow path. Embodiments provide a system and method of heatingsupply air through heated liquid circulating within one or more coils ofa heating device, such as a first pre-heater. Embodiments may alsocapture heat energy from exhaust flue gas, and recycle the heat energyback into the supply air by way of a second pre-heater. Embodimentsprovide a system and method of using heated liquid and recycled flue gasenergy to pre-heat an air stream to reduce the need for defrosting incold conditions. Overall, embodiments provide a highly-efficient DOAS.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments of the disclosure without departing from their scope. Whilethe dimensions and types of materials described herein are intended todefine the parameters of the various embodiments of the disclosure, theembodiments are by no means limiting and are exemplary embodiments. Manyother embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the various embodiments ofthe disclosure should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second,” and “third,” etc. are used merely as labels,and are not intended to impose numerical requirements on their objects.Further, the limitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. §112, sixth paragraph, unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

This written description uses examples to disclose the variousembodiments of the disclosure, including the best mode, and also toenable any person skilled in the art to practice the various embodimentsof the disclosure, including making and using any devices or systems andperforming any incorporated methods. The patentable scope of the variousembodiments of the disclosure is defined by the claims, and may includeother examples that occur to those skilled in the art. Such otherexamples are intended to be within the scope of the claims if theexamples have structural elements that do not differ from the literallanguage of the claims, or if the examples include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

1. An energy exchange system comprising: an energy recovery deviceconfigured to be disposed within supply and exhaust air flow paths; atleast one first pre-heater configured to be positioned within one orboth of the supply and exhaust air flow paths, wherein the at least onepre-heater comprises one or more coils configured to circulate a firstliquid that is configured to transfer heat to air within the one or bothof the supply and exhaust air flow paths; and at least one boileroperatively connected to the at least one first pre-heater, wherein theat least one boiler is configured to heat the first liquid.
 2. Theenergy exchange system of claim 1, wherein the at least one firstpre-heater is configured to be upstream of the energy recovery devicewithin the supply air flow path.
 3. The energy exchange system of claim1, further comprising a heater configured to be downstream of the energyrecovery device within the supply air flow path.
 4. The energy exchangesystem of claim 3, wherein the at least one first pre-heater isconfigured to be positioned within the supply air flow path.
 5. Theenergy exchange system of claim 1, wherein the at least one boilercomprises a main tank configured to retain the first liquid, and aheating element configured to heat the first liquid.
 6. The energyexchange system of claim 1, wherein the at least one first pre-heatercomprises multiple first pre-heaters configured to be positioned withinthe supply air flow path.
 7. The energy exchange system of claim 6,wherein the multiple pre-heaters are operatively connected to the atleast one boiler.
 8. The energy exchange system of claim 7, wherein theat least one boiler comprises multiple boilers, wherein the each of themultiple boilers is operatively connected to one of the multiple firstpre-heaters.
 9. The energy exchange system of claim 1, furthercomprising: at least one second pre-heater configured to pre-heat airwithin one or both of the supply and exhaust air flow paths; a heaterconfigured to be disposed within the supply air flow path, wherein theheater is configured to generate flue gas; and a heat transfer deviceoperatively connected to the heater and the at least one secondpre-heater, wherein the heat transfer device is configured to receiveenergy from the flue gas from the heater and transfer heat from the fluegas to a second liquid within the heat transfer device, and wherein thesecond liquid is configured to be channeled to the at least one secondpre-heater so that heat is transferred from the second liquid to supplyair within the supply air flow path before the supply air encounters theenergy recovery device.
 10. The system of claim 9, wherein the heater isconfigured to be downstream from the energy recovery device within thesupply air flow path.
 11. The system of claim 9, wherein the heater isconfigured to be upstream from the energy recovery device within thesupply air flow path.
 12. The system of claim 9, wherein the at leastone first pre-heater is configured to be positioned with the supply airflow path.
 13. The system of claim 9, further comprising one or more ofpipes, tubes, conduits, or plenum connected between the heat transferdevice and the heater, wherein the flue gas is configured to pass fromthe heater to the heat transfer device via the one or more of pipes,tubes, conduits, or plenum.
 14. The system of claim 1, wherein theenergy exchange system is a Dedicated Outdoor Air System (DOAS).
 15. Thesystem of claim 1, wherein the energy recovery device is one or more ofan enthalpy wheel, a sensible wheel, a desiccant wheel, a plate heatexchanger, a plate energy exchanger, a heat pipe, or a run-around loop.16. The system of claim 1, wherein the one or more coils are configuredto be disposed within or around a portion of the supply air flow path.17. The system of claim 1, further comprising at least one return airduct configured to fluidly connect the supply air flow path with theexhaust air flow path.
 18. The system of claim 1, further comprising atleast one bypass duct configured to be disposed within the supply airflow path, wherein the at least one bypass duct is configured to bypassat least a portion of the supply air around one or both of the at leastone first pre-heater or the energy recovery device.
 19. A method ofoperating an energy exchange system having a supply air flow path thatallows supply air to be supplied to an enclosed structure and an exhaustair flow path that allows exhaust air from the enclosed structure to beexhausted to the atmosphere, the method comprising: heating a firstliquid within an internal chamber of a boiler; pumping the first liquidfrom the boiler to at least one first pre-heater disposed within one orboth of the supply air flow path and the exhaust air flow path;pre-heating air within the one or both of the supply air flow path andthe exhaust air flow path with the first liquid within the at least onefirst pre-heater; and pumping the first liquid from the at least onefirst pre-heater back to the boiler.
 20. The method of claim 19, furthercomprising: capturing flue gas generated by a heater; channeling theflue gas to a heat transfer device; transferring heat from the flue gasto a second liquid within the heat transfer device; circulating thesecond liquid to at least one second pre-heater disposed within one orboth of the supply air flow path and the exhaust air flow path; andtransferring heat within the second liquid to the air within one or boththe supply air flow path and the exhaust air flow path.
 21. The methodof claim 20, further comprising venting the flue gas from the heattransfer device after heat from the flue gas has been transferred to thesecond liquid within the heat transfer device.
 22. The method of claim20, further comprising recirculating the second liquid back to the heattransfer device after the heat within the second liquid has beentransferred to the supply air.
 23. The method of claim 20, furthercomprising passing the pre-heated air to an energy recovery device. 24.The method of claim 20, further comprising bypassing at least a portionof the air around the at least one first pre-heater.
 25. A DedicatedOutdoor Air System (DOAS) comprising: a heater configured to be disposedwithin a supply air flow path; a first pre-heater configured to beupstream from the heater within the supply air flow path, wherein thefirst pre-heater is configured to pre-heat the supply air through heattransfer with a first liquid that circulates through the firstpre-heater; and a boiler operatively connected to the first pre-heater,wherein the boiler is configured to heat the first liquid.
 26. The DOASof claim 24, further comprising: a second pre-heater configured to beupstream from the heater within the supply air flow path; and a heattransfer device operatively connected to the heater and the secondpre-heater, wherein the heat transfer device is configured to receiveflue gas from the heater and transfer heat from the flue gas to a secondliquid within the heat transfer device, and wherein the second liquid isconfigured to be channeled to the second pre-heater so that heat istransferred from the second liquid to supply air within the supply airflow path.